CN115198182B - Ti-containing duplex stainless steel and manufacturing method thereof - Google Patents
Ti-containing duplex stainless steel and manufacturing method thereof Download PDFInfo
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- CN115198182B CN115198182B CN202210767401.4A CN202210767401A CN115198182B CN 115198182 B CN115198182 B CN 115198182B CN 202210767401 A CN202210767401 A CN 202210767401A CN 115198182 B CN115198182 B CN 115198182B
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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- C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
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- C22C33/06—Making ferrous alloys by melting using master alloys
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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Abstract
The invention provides a Ti-containing duplex stainless steel, which comprises the following components in parts by mass: 0.015 to 0.050 percent of C; mn 0.8-1.5%; si 0.2-0.5%; 24.0 to 26.0 percent of Cr; 4.50 to 6.50 percent of Ni; 0.35 to 0.60 percent of Ti; n is 0 to 0.030 percent; p is 0 to 0.025 percent; s is 0 to 0.015 percent; 0 to 0.05 percent of Al; the invention further discloses a manufacturing method of the duplex stainless steel, which comprises the steps of vacuum induction casting of electrode rods, electroslag remelting of steel ingots, forging cogging, hot rolling of finished products and solution treatment, and solves the problems that the conventional duplex stainless steel is common in mechanical strength, easy to break, easy to passivate and easy to crack on the surface.
Description
Technical Field
The invention relates to the field of stainless steel manufacturing, in particular to a Ti-containing duplex stainless steel and a manufacturing method thereof.
Background
The austenitic+ferritic duplex stainless steels used in engineering are mostly duplex stainless steels based on austenite and containing not less than 30% ferrite, most often about 50% each of the two phases. The duplex stainless steel of austenite and ferrite has the characteristics of both austenitic and ferritic stainless steel, and compared with ferritic steel, the duplex stainless steel of ferrite has the characteristics of higher plasticity and toughness, no room-temperature brittleness, improved intergranular corrosion resistance and welding performance, high brittleness at 475 ℃ and heat conductivity coefficient, small expansion coefficient, good oxidation resistance, superplasticity and the like. Compared with austenitic stainless steel, the strength is high, and the intergranular corrosion resistance and the chloride stress corrosion resistance are obviously improved. The duplex stainless steel is also a nickel-saving stainless steel. The duplex stainless steel has the main characteristics that the yield strength can reach 400-550MPa, which is 2 times of that of the common austenitic stainless steel, so that the duplex stainless steel can save materials and reduce the manufacturing cost of equipment. In the aspect of corrosion resistance, particularly under the condition of severe medium environment (such as seawater and high chloride ion content), the duplex stainless steel has obviously better pitting corrosion resistance, crevice corrosion resistance, stress corrosion resistance and corrosion fatigue resistance than the common austenitic stainless steel, and can be compared favorably with high alloy austenitic stainless steel. The duplex stainless steel is widely applied to the industrial fields of petrochemical equipment, seawater and wastewater treatment equipment, oil and gas transmission pipelines, papermaking and the like due to the special advantages, is also researched in the bridge bearing structure field in recent years, and has good development prospect.
The common duplex stainless steel is 1Cr21Ni5Ti, and the mass percentages of chemical elements of the 1Cr21Ni5Ti duplex stainless steel are shown in table 1:
TABLE 1 chemical element mass percent%
The production method of the steel grade comprises the following steps: vacuum induction casting electrode rod, electroslag remelting, forging and cogging, rolling into a finished product, solid solution and qualified delivery inspection.
The steel grade has the following problems in production: the existing steel has high C content, the steel also contains higher Ti, the Ti is a strong carbonization forming element, the C in the steel is easy to form TiC with the Ti, and the residual N and Ti in the steel also form TiN and composite Ti (C, N) inclusion. These inclusions are hard and brittle particles which are easily aggregated, and if they are aggregated in the interior of the steel, they will cause the toughness of the steel to be reduced, and in severe cases, the product will be brittle, and if they are aggregated, they will be brittleOn the surface of the steel ingot, cracks, forging cracks and the like are generated on the surface during forging; the heat processing plasticity of the duplex stainless steel is relatively poor compared with that of the duplex stainless steel taking ferrite as a matrix, which is mainly caused by different deformation modes of ferrite and austenite during heat processing, the austenite content in the existing steel type 1Cr21Ni5Ti is about 50 percent, the main softening process during the deformation of the ferrite steel is dynamic recovery by strain, the main softening process of the austenitic stainless steel is dynamic recrystallization, the softening process of the ferrite phase is prior to the austenite phase, the ferrite is equivalent to a soft phase, and the austenite is equivalent to a hard phase; the prior steel has high carbon content (0.09-0.14%) of 1Cr21Ni5Ti and inferior corrosion resistance as low as carbon content (less than or equal to 0.015-0.05%), mainly because C is a strong carbide forming element and forms Cr with Cr 23 C 6 The periphery of the carbide is lean in Cr, cr is a main element in the stainless steel, and Cr reduces the passivation current of the steel, so that the duplex stainless steel is easy to passivate, the stability of a passivation film is maintained, the repairing capability of the damaged passivation film can be improved, the repassivation capability of the steel is enhanced, and the corrosion resistance of the steel is ensured; when the conventional steel type 1Cr21Ni5Ti is subjected to intergranular corrosion test, a sample needs to be bent (bent by 90 degrees) after corrosion, a fracture phenomenon often occurs during bending, and after fracture occurs, structural observation is required through a metallographic method, so that the fracture is proved not to be caused by corrosion, and although the intergranular corrosion test item can be proved to be qualified from the basis of intergranular corrosion judgment, the surface cracks and fractures can cause problems during product delivery.
Disclosure of Invention
The invention aims to provide a Ti-containing duplex stainless steel, which aims to solve the problems that the conventional duplex stainless steel has common toughness, is easy to break after an intergranular corrosion sample is bent and has low corrosion resistance.
In order to solve the problems, the invention provides a Ti-containing duplex stainless steel, which comprises the following components in parts by mass: 0.015 to 0.050 percent of C; mn 0.8-1.5%; si 0.2-0.5%; 24.0 to 26.0 percent of Cr; 4.50 to 6.50 percent of Ni; 0.35 to 0.60 percent of Ti; n is 0 to 0.030 percent; p is 0 to 0.025 percent; s is 0 to 0.015 percent; 0 to 0.05 percent of Al; the balance being Fe and other unavoidable impurities.
The preferable scheme comprises the following components in percentage by mass: 0.018 to 0.040 percent; mn 0.9-1.4%; si 0.25-0.45%; 24.5 to 25.8 percent of Cr; 5.00 to 6.20 percent of Ni; 0.42 to 0.55 percent of Ti; n is 0 to 0.025 percent; p is 0 to 0.020 percent; s is 0 to 0.010 percent; 0 to 0.04 percent of Al; the balance being Fe and other unavoidable impurities.
The preferable scheme comprises the following components in percentage by mass: 0.025 percent of C; mn 1.20%; si 0.40%; 25.6% of Cr; 5.70% of Ni; 0.50% of Ti; n is 0 to 0.025 percent; p is 0 to 0.020 percent; s is 0 to 0.010 percent; 0.035% of Al; the balance being Fe and other unavoidable impurities. The design principle of the Ti-containing duplex stainless steel is as follows:
the properties of duplex stainless steel in stress corrosion cracking resistance are closely related to the main phase composition (i.e. the balance ratio of austenite and ferrite, also called phase ratio), which in turn depends to a large extent on the composition of the steel and the heating temperature, the composition design of the Ti-containing duplex stainless steel according to the invention is as follows:
the element C is an austenite forming element, and generally, as the content of the element C increases, the strength and hardness of the steel increase, but the corrosion resistance and toughness decrease. The duplex stainless steel mainly considers that the corrosion resistance is required to be met and the good matching of strength and toughness is required, so that the carbon control is relatively low, and the strength is improved by adding Ti element and controlling rolling. The C content of the duplex stainless steel containing Ti is controlled between 0.015 and 0.05 percent.
Mn element is both an enlarged austenite element and a stabilized austenite element, and Mn also has the effects of desulfurization and deoxidation in steel. The dual-phase stainless steel containing Ti mainly considers the action of balancing ferrite and austenite structures and cannot be controlled to be too high, so that Mn element is controlled to be in the range of 0.8-1.5%.
The Cr element is ferrite forming element, the content of the Cr element is high, and the corrosion resistance of the steel can be improved, the Ti-containing duplex stainless steel is a duplex stainless steel taking ferrite as a matrix, and the Cr element cannot be controlled to be too low in order to balance the structure, so that the Cr element content of the Ti-containing duplex stainless steel is controlled to be between 24.0 and 26.0 percent.
The Ni element is an austenite forming element, and in the design of the duplex stainless steel, a certain amount of Ni is added in consideration of ensuring that a certain amount of austenite is obtained, and the duplex steel itself is a nickel-saving steel, so that Ni is not more than 8% in general, the Ti-containing duplex stainless steel of the present invention controls the content of the austenite in addition to Ni, and also takes the action of C, N, mn into consideration, and the Ti-containing duplex stainless steel of the present invention controls the content of the Ni element to be between 4.50 and 6.5% in consideration of the synergistic action between the elements.
The Ti element is a ferrite forming element and is also a strong deoxidizing element. Ti has the main function of forming TiC with C in the duplex stainless steel containing Ti and reducing Cr formation 23 C 6 Thereby reducing the phenomenon of poor Cr in grain boundary and improving the intergranular corrosion resistance of the steel; the Ti has the additional function of refining grains and improving the strength of steel. The dual-phase stainless steel containing Ti controls the content of Ti element to be between 0.35 and 0.60 percent.
The Si element belongs to ferrite forming elements and plays a certain role in deoxidizing the steel. The steel of the invention contains Ti, which is a strong deoxidizing element, and the Si content in the steel has little influence on the duplex stainless steel containing Ti and can be controlled to be low, so that the Si content is controlled to be between 0.2 and 0.5 percent.
The Al element is a ferrite forming element and is also a strong deoxidizing element. The deoxidizing ability of Al is inferior to that of Ti. This element is not desirable in the duplex stainless steel containing Ti, and the purpose is to prevent formation of hard and brittle spots such as AlN and TiN, increase the content of inclusions in the steel and affect the plasticity of the steel. The dual-phase stainless steel containing Ti controls the content of Al element to be less than or equal to 0.05 percent.
The N element acts similarly to the carbon element and is also an austenite forming element, and the N element is an inexpensive austenite forming element and exists in the atmosphere. The N element in the steel can improve the strength of the steel, and the plasticity is not reduced. In the Ti-containing duplex stainless steel, because Ti element is included, in order to reduce formation of TiN inclusion, N is controlled as low as possible, and the N element content of the Ti-containing duplex stainless steel is required to be controlled to be less than or equal to 0.030%.
S, P is an impurity element, and the lower the content in the steel is, the better, but in view of the raw material cost and smelting cost, the content of S element is controlled to be less than 0.015% and the content of P element is controlled to be less than 0.025% in the duplex stainless steel containing Ti.
The invention provides a ferrite-austenite duplex stainless steel with titanium and good strength and toughness, which is a duplex stainless steel taking ferrite as a matrix, wherein main alloy elements are Cr, ni and Ti, and the corrosion resistance is obviously higher than that of the existing steel 1Cr21Ni5Ti by reducing the content of C; the duplex stainless steel containing Ti has obviously higher cold and hot processing performance than the existing steel grade by controlling the phase proportion; the fine grain structure can be obtained by controlled rolling (rolling in a dual phase zone) and heat treatment, so that both the strength and toughness of the steel are improved. The Ti-containing duplex stainless steel can be manufactured into forging pieces, bars, plates, pipes, cold drawn materials and the like, and the product can be popularized and used in industries such as petroleum, chemical industry, seawater purification, sewage treatment and the like.
The invention aims to provide the manufacturing method of the double-phase stainless steel containing Ti, so as to solve the problem that the double-phase stainless steel prepared by the conventional manufacturing method is poor in strength and toughness.
In order to solve the above problems, the present invention provides a method for manufacturing a Ti-containing duplex stainless steel, comprising the steps of:
s1: vacuum induction casting electrode rod: after furnace charge is melted down, argon is introduced into the furnace, ferrosilicon, metallic titanium and metallic manganese are sequentially added into the furnace, the furnace temperature is controlled to be 1510-1530 ℃, refining treatment is carried out, tapping is carried out after refining is finished, molten steel is poured into an electrode, and demoulding and air cooling are carried out after mould cooling to obtain an electrode rod; the furnace burden comprises metal chromium, nickel plates and pure iron;
s2: electroslag remelting steel ingot: performing electroslag remelting on the electrode rod obtained by the treatment in the step S1, wherein the slag system of the electroslag remelting is CaF 2 With Al 2 O 3 Is subjected to mold cooling after electroslag remelting is finishedTreating, demoulding and air cooling to obtain an electroslag ingot;
s3: forging and cogging: and (3) heating the electroslag ingot obtained in the step (S2) to 1170-1190 ℃, forging and cogging, and air-cooling after forging and cogging to obtain a blank.
S4: hot rolling into a product: heating the blank subjected to air cooling in the step S3 to 1070-1090 ℃ and then rolling, and cooling after rolling to obtain a bar;
s5: solution treatment: and (3) heating the bar cooled in the step (S4) to 920-950 ℃, preserving heat for 1-1.5h, and cooling to obtain the Ti-containing duplex stainless steel.
In the step S1, the refining treatment time is more than or equal to 40 minutes, and before tapping, when the argon pressure in the furnace reaches 6KPa, metal manganese is added; the tapping temperature is 1450-1470 ℃, and the mold cooling time is more than or equal to 10 hours.
In the preferred scheme, in the step S2, before the electrode rod is subjected to electroslag remelting, electrode surface grinding is required, and after the electrode rod surface is ground to the original color of visible metal, electroslag remelting is started.
Preferably, in the step S2, the CaF 2 With Al 2 O 3 The mass ratio of (2) is 70:30.
Preferably, in the step S2, the method further comprises adding TiO 2 And the operation of Al into the electrode rod, wherein the adding time of the Al is 1/3 of the melting time of the electrode rod.
In the step S3, the initial temperature of the electroslag ingot is less than or equal to 600 ℃, the heating rate of heating is less than or equal to 100 ℃/h, the finishing temperature is more than or equal to 900 ℃, and the heat preservation time of the step S3 is 2-3 h; in the step S4, the initial temperature of the blank is less than or equal to 600 ℃, the heating rate of heating is less than or equal to 100 ℃/h, the finishing temperature is more than or equal to 900 ℃, and the heat preservation time of the step S4 is 0.5-1h. .
In a preferable mode, in the step S5, the initial temperature of the steel ingot is equal to or less than 600 ℃, the temperature rising speed is equal to or less than 80 ℃, and the cooling mode is water cooling.
Compared with the prior art, the invention has the following advantages due to the adoption of the technical scheme:
compared with the existing steel type 1Cr21Ni5Ti, the duplex stainless steel has low C content, less formed carbide and high corrosion resistance. The carbon content is low, the strength is low, but a fine grain structure can be obtained through a special rolling process, so that the strength is improved, the dual-phase steel has good plasticity, and the aim of designing the dual-phase steel is fulfilled; in the actual production, the surface of 1Cr21Ni5Ti has more cracks, and in order to ensure the surface quality when rolling small round bars, the specifications are enlarged for rolling, and then the delivery size and the surface quality can be met through peeling. This affects not only the yield but also the production efficiency. The dual-phase stainless steel containing Ti is the dual-phase stainless steel taking ferrite as a matrix, and has more ferrite and good processing plasticity at high temperature; conventional 1Cr21Ni5Ti duplex stainless steel has a relatively large austenite content at high temperatures. Austenite is a hard phase and ferrite is a soft phase, so that the duplex stainless steel containing Ti according to the present invention has better hot workability than conventional duplex stainless steel.
Drawings
FIG. 1 is a steel phase diagram of the present invention;
fig. 2 is a drawing showing a cogging heating curve of a steel ingot of the present invention;
FIG. 3 is a graph showing the rolling heating curve of the steel of the present invention;
FIG. 4 is a graph showing the solid solution temperature of the steel of the present invention.
Detailed Description
The following description of the present invention will be made clearly and fully, and it is apparent that the embodiments described are some, but not all, of the embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention provides a dual-phase stainless steel containing Ti, which is required to reduce the contents of interstitial elements such as carbon, nitrogen and the like and other impurities in the steel as much as possible, strictly control the chemical components of the steel, ensure proper phase ratio, and control the chemical components of each element in an electrode rod according to the requirements in table 2 in consideration of burning loss and component fluctuation of easily oxidized element Ti in the electroslag remelting process:
table 2:
the manufacturing method of the duplex stainless steel containing Ti comprises the following steps:
s1: vacuum induction casting electrode rod: after furnace charge is melted down, argon is introduced into the furnace, ferrosilicon, metallic titanium and metallic manganese are sequentially added into the furnace, the furnace temperature is controlled to be 1510-1530 ℃, refining treatment is carried out, tapping is carried out after refining is finished, molten steel is poured into an electrode, and demoulding and air cooling are carried out after mould cooling to obtain an electrode rod; the furnace burden comprises metal chromium, nickel plates and pure iron;
the step S1 comprises the following points:
selecting raw materials with low impurity content such as C, S, P, N, wherein all furnace materials are oilless and dried, the surfaces of pure iron and nickel plates are polished and bright, and the steel grade is smelted under the good condition of a furnace body;
in order to sufficiently remove C, O, N and other impurities, high-temperature boiling refining is adopted, the refining temperature is controlled between 1510 and 1530 ℃, and the refining time is more than or equal to 40 minutes;
before tapping, the temperature of molten steel is controlled within the range of 1450-1470 ℃;
in order to reduce volatilization of manganese under vacuum, adding metal manganese after filling Ar (more than or equal to 6 KPa);
the induction electrode is cast without riser, and no exothermic agent such as feeding materials such as carbonized rice hulls and the like are placed;
and casting an electrode with phi of 260mm, and demoulding and air cooling after mould cooling is more than or equal to 10 hours.
S2: electroslag remelting steel ingot: grinding the surface of the electrode rod until the metal is natural, and then carrying out electroslag remelting; electroslag remelting is carried out on the electrode rod obtained by the grinding treatment, and the slag system of the electroslag remelting is CaF 2 With Al 2 O 3 After electroslag remelting is finished, carrying out mold cooling treatment, and carrying out air cooling after demolding to obtain an electroslag ingot;
the step S2 comprises the following points:
electroslag crystallizer: phi 360mm;
slag CaF 2 :Al 2 O 3 =70:30 binary slag system, slag amount 42±2kg;
to reduce the burning loss of Ti element, 300 to 400 g of Tio is added into the slag 2 After melting 1/3 electrode rod, adding 300-400 g of Al powder;
smelting voltage is 50-55V, and current is 7000-10000A;
demoulding and air cooling after the electroslag ingot is cooled for more than or equal to 2 hours.
S3: forging and cogging: and (3) heating the electroslag ingot obtained in the step (S2) to 1170-1190 ℃, forging and cogging, and air-cooling after forging and cogging.
For Cr-Ni based stainless steel, the single phase structure is more plastic than the dual phase structure, and the pure ferritic steel is more plastic than the austenitic steel. As shown in fig. 1, when the temperature is heated to 1150 ℃, austenite is completely transformed into ferrite, and the ferrite becomes a single-phase ferrite structure after the temperature is higher than 1150 ℃, at this time, the steel has good thermoplasticity, and the ferrite is coarse in consideration of the overhigh temperature, and is unfavorable for obtaining a fine crystal structure by subsequent rolling, so the heating temperature for steel ingots is controlled to 1170-1190 ℃; under the condition of ensuring plastic deformation, the forging is easy to adopt low final forging temperature. However, the temperature should not be too low, and if it is lower than the recrystallization temperature, an abnormally large grain structure is liable to occur, so that the final forging temperature is controlled to be not less than 900 ℃ in order to obtain relatively uniform and finer grains. The specific process is shown in fig. 2.
The step S3 comprises the following points:
the steel ingot is heated to be required to be uniformly and thoroughly burned, in the forging process, small deformation forging is started, and after the as-cast structure is broken, the steel ingot is forged by larger deformation as much as possible, under the condition of ensuring plastic deformation, the lower final forging temperature is preferably controlled, and simultaneously, the firing time is preferably reduced as much as possible, so that good fine crystal structure can be obtained, and good structure assurance is provided for the follow-up forging.
S4: hot rolling into a product: heating the steel ingot subjected to air cooling in the step S3 to 1070-1090 ℃ and then rolling, and cooling after rolling to obtain a bar;
besides corrosion resistance, strength and toughness are required, besides control of components, a rolling process is also required to be controlled, and the steel is ferrite+austenite duplex stainless steel taking ferrite as a matrix, and rolling is performed in a duplex region to obtain a fine grain structure.
The step S4 comprises the following points:
the key point of the rolling process is to control the heating temperature and the finishing temperature, according to the analysis, the thermoplastic is preferably a single-phase region, and the ferrite is better than the austenite plasticity, but the temperature which is the same as that of the cogging of the steel ingot is selected for heating (1180 ℃ +/-10 ℃), the grain size of the final product is very large, some products reach about grade 2, and the performance can not meet the design requirement.
In order to obtain a fine grain structure of the dual phase steel, the heating temperature should be controlled near the (austenite and ferrite)/ferrite transformation point (key point), and a suitable holding time is selected according to the size of the heated blank, and is not suitable to be too long, so as to ensure the original ferrite structure that the ferrite grain size has not grown before rolling. According to the phase diagram (see fig. 1) of the steel of the present invention, all deformation is completed in the two-phase region of 900-1050 ℃, so that the heating temperature is controlled at 1090 ℃ +/-10 ℃; considering that the finishing temperature cannot be lower than the recrystallization temperature, the finishing temperature is controlled to be above 900 ℃;
after rolling, the steel is required to be rapidly cooled, the steel can be cooled by water under the condition that the steel can be cooled by air under the condition that the steel is not allowed to be piled for cooling, and the brittleness at 475 ℃ and sigma phase brittleness are prevented;
the rolling and heating process of the dual-phase steel comprises the following steps: 1090+/-10 ℃ and the final rolling temperature is more than or equal to 900 ℃, and the specific heating process is shown in figure 3.
S5: solution treatment: and (3) heating the bar cooled in the step (S4) to 920-950 ℃, preserving heat for 1-1.5h, and cooling to obtain the Ti-containing duplex stainless steel.
The purpose of the solution treatment is to make carbide and precipitation equally solid-dissolved into the dual-phase steel matrix, and then rapidly water-cooled, so that the corrosion resistance is ensured and the good matching of strength and toughness is ensured. The steel of the invention belongs to ferrite and austenite duplex stainless steel taking ferrite as a matrix. The solid solution temperature has obvious influence on the duplex stainless steel taking the ferrite as a matrix, the temperature is high, the solid solution of carbide is sufficient, the ferrite content is increased, crystal grains are easy to grow up, and finally the strength and the toughness are influenced; if the temperature is low, the carbide cannot be completely dissolved in the solution, and the corrosion resistance is lowered.
Therefore, in order to ensure the full solid solution and prevent the growth of grains, the solid solution temperature is controlled within the range of 920-950 ℃, the solid solution time is controlled within 1-1.5h, and the sigma phase is prevented from being precipitated, and the furnace is rapidly cooled after discharging. The specific process is shown in fig. 4.
The following description and additions are made to the above-described embodiments of the present invention in conjunction with the data:
example 1:
the embodiment provides a duplex stainless steel containing Ti, which comprises the following components:
the composition comprises the following components: 0.019 percent of C; mn 1.27%; 0.36% of Si; 24.80% of Cr; 6.06 percent of Ni; 0.42% of Ti; n is 0.025; p is 0.016; s is 0.004%; 0.035% of Al; the balance being Fe and other unavoidable impurities.
The embodiment provides a method for manufacturing a duplex stainless steel containing Ti, which comprises the following steps:
s1: vacuum induction casting electrode rod: after furnace charge is melted, argon is introduced into the furnace, ferrosilicon and metallic titanium are sequentially added into the furnace, when the pressure of the argon in the furnace reaches 6KPa, metallic manganese is added, the furnace temperature is controlled to be 1510-1530 ℃, refining treatment is carried out, the refining treatment time is more than or equal to 40 minutes, steel is tapped after refining, the tapping temperature is 1450-1470 ℃, molten steel is poured into phi 260mm electrodes, the electrode bars are obtained by demoulding and air cooling after mould cooling, and the mould cooling time is more than or equal to 10 hours, wherein the furnace charge comprises metallic chromium, nickel plates and pure iron;
s2: electroslag remelting steel ingot: grinding the electrode rod obtained in the step S1 to obtain an electrode rod surface, starting electroslag remelting after grinding until the surface of the electrode rod is visible to have the metallic natural color, adding 300-400 g of TiO2 powder into the electroslag, melting 1/3 of the electrode rod, adding 300-400 g of Al powder, and obtaining the slag system of CaF remelting 2 With Al 2 O 3 The slag quantity is 42+/-2 kg; the CaF is 2 With Al 2 O 3 The mass ratio of the alloy is 70:30, mold cooling treatment is carried out after electroslag remelting is finished, and air cooling is carried out after demolding to obtain an electroslag ingot;
s3: forging and cogging: and (2) heating the electroslag ingot obtained in the step (S2) to 1180 ℃, forging and cogging, wherein the initial temperature of the electroslag ingot is 550 ℃, the heating rate of heating is 80 ℃/h, the final rolling temperature is 920 ℃, the heat preservation time is 2.5h, and air cooling is performed after forging and cogging.
The steel is ferrite and austenite duplex stainless steel taking ferrite as a matrix, and has high ferrite content, good hot working plasticity and heating temperature rise. The ferrite content gradually increases and finally turns into single-phase ferrite. However, the temperature is high, ferrite is coarse, in order to prevent coarse ferrite, the cogging heating temperature of the steel ingot is controlled to 1180+/-10 ℃, the final forging temperature is controlled to be more than or equal to 900 ℃, and air cooling is carried out after forging.
The steel ingot is heated to be required to be uniformly and thoroughly burned, in the forging process, small deformation forging is started, and after the as-cast structure is broken, the steel ingot is forged by larger deformation as much as possible, under the condition of ensuring plastic deformation, the lower final forging temperature is preferably controlled, and simultaneously, the firing time is preferably reduced as much as possible, so that good fine crystal structure can be obtained, and good structure assurance is provided for the follow-up forging.
S4: hot rolling into a product: heating the steel ingot subjected to air cooling in the step S3 to 1080 ℃, rolling the steel ingot, wherein the initial temperature of the steel ingot is 600 ℃, the heating rate of heating is 70 ℃/h, the final rolling temperature is 930 ℃, the heat preservation time is 2.5h, and cooling after rolling;
after forging and cogging, the surface of the blank needs to be polished, and the blank is reheated in a chamber-shaped furnace for rolling. For the duplex stainless steel taking ferrite as a matrix, the heating temperature is not too high to prevent coarse grains, so that the heating temperature of the blank during reheating and rolling is controlled within the range of 1090+/-10 ℃; in order to obtain a fine-grained structure, the deformation should be done in the biphasic region of 900-1050 ℃. I.e. the maximum initial rolling temperature is not more than 1050 ℃, and the minimum initial rolling temperature is not less than 900 ℃. As the deformation proceeds, dispersed and fine austenite particles are precipitated on the ferrite matrix, particularly at 900 to 950 ℃. The austenite precipitation rate is the fastest, so the final rolling temperature is controlled between 900 ℃ and 940 ℃.
During rolling, the time between each pass is as short as possible, so that the grains do not grow up in the dynamic recrystallization or dynamic recovery interval. After rolling, the alloy is required to be cooled rapidly, the alloy can be cooled by water under the condition that the alloy is not cooled by air, and stacking cooling is not allowed, so that 475 ℃ brittleness and sigma phase brittleness are prevented.
S5: solution treatment: and (3) heating the bar cooled in the step (S4) to 920 ℃, preserving heat for 1.5 hours, wherein the initial temperature of the steel ingot is 200 ℃, the heating speed is equal to 80 ℃, the cooling mode is water cooling, and the double-phase stainless steel containing Ti is obtained after cooling.
The steel belongs to ferrite and austenite duplex stainless steel with ferrite as a matrix, the solid solution temperature has obvious influence on the ferrite and austenite duplex stainless steel with the matrix, the temperature is high, the solid solution of carbide is sufficient, the ferrite content is increased, crystal grains are easy to grow up, and finally the strength and the toughness are influenced; if the temperature is low, the carbide cannot be completely dissolved in the solution, and the corrosion resistance is lowered. Therefore, in order to ensure the full solid solution and prevent the growth of grains, the solid solution temperature is controlled within the range of 920-950 ℃, the solid solution time is controlled within 1-1.5h, and the sigma phase is prevented from being precipitated, and the furnace is rapidly cooled after discharging.
In the reaction of example 1, the amounts of the raw materials added were as follows:
0.019 percent of C; mn 1.30%; si 0.38%; 24.90% of Cr; 6.10% of Ni; 0.53% of Ti; p is 0.017%; s is 0.010 percent; 0.040% of Al; the balance being Fe and other unavoidable impurities.
Examples 2 to 5 are similar to example 1 except that the Ti-containing duplex stainless steel is different in composition, the heat treatment process of steps S3 to S5 is different, and the amounts of raw materials to be added in the reaction are different, as shown in tables 3 to 6, in particular:
table 3 examples 1-5 mass percent of vacuum induction furnishes chemical composition
Table 4 parameters of the ingot heating process in examples 1 to 5
Table 5 examples 1-5 rolled product process parameters
TABLE 6 solid solution treatment Process of examples 1-5
The chemical components of the finished products of the examples 1-5 obtained after the reaction are as follows in percentage by mass:
the finished products prepared in examples 1 to 5 were subjected to the detection of the relevant mechanical properties, and the detection results are as follows:
TABLE 8 results of Performance test for examples 1-5
For the same detection of the conventional 1Cr21Ni5Ti duplex stainless steel, four samples are selected for detection, and the detection results are as follows:
TABLE 9 results of 1Cr21Ni5Ti test on the prior art product
From comparison of the test results in tables 8 and 9, the strength index of the steel of the present invention is substantially at one level with that of the conventional product, but the yield index of the steel of the present invention is significantly higher than that of the conventional product, and the elongation is substantially at one level, but the surface molding index is significantly higher than that of the conventional product. The strength and toughness of the steel are relatively good.
Intergranular corrosion comparative tests were performed on examples 1 to 5 and conventional product 1Cr21Ni5Ti, and the conditions and results of the tests are shown in table 10:
TABLE 10 comparison of intergranular corrosion test results
From the comparison test of the intergranular corrosion, the intergranular corrosion surface of the embodiment of the invention has no crack, but the conventional product 1Cr21Ni5Ti of the comparison document has the problems of fracture and bending and cracking, which further proves that the duplex stainless steel containing Ti of the invention effectively solves the problems in the background technology.
The steel is a duplex stainless steel with ferrite as a matrix, and has more ferrite and good processing plasticity at high temperature; conventional 1Cr21Ni5Ti duplex stainless steel has a relatively large austenite content at high temperatures. Austenite is a hard phase and ferrite is a soft phase, so that the hot workability of the steel is not as good as that of the steel of the present invention. In the actual production, the surface of 1Cr21Ni5Ti has more cracks, and in order to ensure the surface quality when rolling small round bars, the specifications are enlarged for rolling, and then the delivery size and the surface quality can be met through peeling. This affects not only the yield but also the production efficiency.
The steel and the existing 1Cr21Ni5Ti are subjected to intergranular corrosion test. The test is that after the sample is sensitized by solid solution and 550 ℃, the sample is corroded in acid for 24 hours, and then is taken out to be bent by 90 degrees on a tester, and the surface crack condition after bending is checked, wherein 50% of the sample of the conventional product 1Cr21Ni5Ti steel is broken or the surface of the bent angle is cracked. Such problems occur mainly due to the high carbonitride content of the conventional product, the increased brittleness of the steel, and the increased tendency of austenite to harden during bending deformation, which increases the brittleness of the steel. The steel of the present invention has low carbon content, less hard and brittle spots mainly comprising carbon, high ferrite content and low hardening tendency, so that similar problems do not occur.
The carbon content of the existing steel 1Cr21Ni5Ti is high (0.09-0.14%), and the corrosion resistance is not as low as that of the steel with the carbon content of less than or equal to 0.015-0.05%. This is mainly due to the formation of Cr from C and Cr 23 C 6 Cr is poor around carbide, is a main element for improving corrosion resistance, and the Cr content is reduced in the matrix, so that the corrosion resistance is inevitably reduced.
Therefore, the duplex stainless steel containing Ti prepared by the formula and the manufacturing method is better than the conventional duplex stainless steel in terms of yield, mechanical strength and toughness, and has higher popularization value and commercial value.
Although the present disclosure is described above, the scope of protection of the present disclosure is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the scope of the invention.
Claims (5)
1. The manufacturing method of the Ti-containing duplex stainless steel is characterized by comprising the following components in parts by mass: 0.015 to 0.050 percent of C; mn 0.8-1.5%; si 0.2-0.5%; 24.0 to 26.0 percent of Cr; 4.50 to 6.50 percent of Ni; 0.35 to 0.60 percent of Ti; n is 0 to 0.030 percent; p is 0 to 0.025 percent; s is 0 to 0.015 percent; 0 to 0.05 percent of Al; the balance of Fe and other unavoidable impurities, wherein the duplex stainless steel containing Ti is ferrite and austenite duplex stainless steel taking ferrite as a matrix;
the manufacturing method comprises the following steps:
s1: vacuum induction casting electrode rod: after furnace charge is melted down, argon is introduced into the furnace, ferrosilicon, metallic titanium and metallic manganese are sequentially added into the furnace, the furnace temperature is controlled to be 1510-1530 ℃, refining treatment is carried out, tapping is carried out after refining is finished, molten steel is poured into an electrode, and demoulding and air cooling are carried out after mould cooling are carried out, so that an electrode rod is obtained; the furnace burden comprises metal chromium, nickel plates and pure iron;
s2: electroslag remelting steel ingot: performing electroslag remelting on the electrode rod obtained by the treatment in the step S1, wherein the slag system of the electroslag remelting is CaF 2 With Al 2 O 3 After electroslag remelting is finished, carrying out mold cooling treatment, and carrying out air cooling after demolding to obtain an electroslag ingot;
s3: forging and cogging: heating the electroslag ingot obtained in the step S2 to 1170-1190 ℃, forging and cogging, and air-cooling after forging and cogging to obtain a blank;
s4: hot rolling into a product: heating the blank subjected to air cooling in the step S3 to 1070-1090 ℃ and then rolling, and performing water cooling or air cooling after rolling to obtain a bar;
s5: solution treatment: heating the bar cooled in the step S4 to 920-950 ℃, preserving heat for 1-1.5h, and cooling to obtain the Ti-containing duplex stainless steel;
in the step S1, the refining treatment time is more than or equal to 40 minutes, and before tapping, metal manganese is added when the argon pressure in the furnace reaches 6 kPa; the tapping temperature is 1450-1470 ℃, and the mold cooling time is more than or equal to 10 hours;
in the step S2, the CaF 2 With Al 2 O 3 The mass ratio of (2) is 70:30;
in the step S3, the initial temperature of the electroslag ingot is less than or equal to 600 ℃, the heating rate of heating is less than or equal to 100 ℃/h, the final forging temperature is more than or equal to 900 ℃, and the heat preservation time of the step S3 is 2-3 h; in the step S4, the initial temperature of the blank is less than or equal to 600 ℃, the heating rate of heating is less than or equal to 100 ℃/h, the finishing temperature is more than or equal to 900 ℃, and the heat preservation time of the step S4 is 0.5-1 h;
in the step S5, the initial temperature of the steel ingot is less than or equal to 600 ℃, the temperature rising speed is less than or equal to 80 ℃/h, and the cooling mode is water cooling.
2. The method for producing a Ti-containing duplex stainless steel according to claim 1, comprising the following components in mass ratio: 0.018 to 0.040 percent; mn 0.9-1.4%; si 0.25-0.45%; 24.5 to 25.8 percent of Cr; 5.00 to 6.20 percent of Ni; 0.42 to 0.55 percent of Ti; n is 0 to 0.025 percent; p is 0 to 0.020 percent; s is 0 to 0.010 percent; 0 to 0.04 percent of Al; the balance being Fe and other unavoidable impurities.
3. The method for producing a Ti-containing duplex stainless steel according to claim 2, comprising the following components in mass ratio: 0.025 percent of C; mn 1.20%; si 0.40%; 25.6% of Cr; 5.70% of Ni; 0.50% of Ti; n is 0 to 0.025 percent; p is 0 to 0.020 percent; s is 0 to 0.010 percent; 0.035% of Al; the balance being Fe and other unavoidable impurities.
4. The method according to claim 1, wherein in the step S2, the electrode rod is subjected to electrode surface grinding before electroslag remelting, and the electroslag remelting is started after grinding until the electrode rod surface is visible in the natural metal color.
5. The method for producing a Ti-containing duplex stainless steel according to claim 1, wherein in said step S2, tiO is further added 2 And the operation of Al into the electrode rod, wherein the adding time of the Al is 1/3 of the melting time of the electrode rod.
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